Management of migratory Helicoverpa spp. moths in Australia

The two major pest species of Helicoverpa in Australia are 'H. armigera' and 'H. punctigera'. Both are capable of long distance migration, but despite considerable research, uncertainty surrounds the frequency, extent and patterns of migration. 'H. armigera' has been characterised as a facultative migrant, leaving cropping areas only when conditions are unfavourable, and often overwintering there. 'H. punctigera', by contrast, has been regarded as an obligate migrant, breeding in winter on native hosts in remote areas of inland Australia and migrating to cropping areas in the south and east every spring, when these hosts senesce with the onset of hot, dry weather. These differences have been invoked to explain differences in seasonal phenology and tendencies to develop resistance to insecticides and transgenic crops. However, recent trends have cast some doubt on these assumptions. Eastern Australia, and particularly inland regions, was affected by an unprecedented drought from 2001 to 2008, and this may have changed the capacity of inland regions to support H. punctigera populations or the migratory behaviour of the pests. Similarly, extensive deployment of transgenic (Bt) cotton in the eastern cropping areas may have affected the season population dynamics of both species. Understanding medium to long term changes in the migration systems of these pests is crucial for developing forecasting techniques for the crops affected (including many grains, oilseeds and cotton), and for devising Resistance Management Plans for Bt cotton.